Regulation of Glomerular Filtration Rate. Renal Clearance 1 Flashcards
What are Starling Forces?
The mechanisms that control glomerular filtration.
What the the factors controlling Starling Forces?
- Hydrostatic P of blood in the glomerular capillaries (Pgc)
- Hydrostatic P of ultrafiltrate in the Bowman’s space (Pbs)
- Oncotic pressure of blood (plasma) in glomerular capillaries (πgc)
(mean value 32 mmHg) - oncotic pressure of ultra filtrate in Bowman’s capsule (πbs) - negligible
What is the importance of having increased oncotic P of plasma in the peritubular capillaries?
facilitates fluid reabsorption from ISF
Where does reabsorption take place in nephron. Which vessels?
peritubular capillaries
What is filtration coefficient (Kf)?
the product of water permeability of the glomerular capillary wall & effective filtration surface area of GM
What does filtration coefficient depend on?
Water permeability per unit surface area (hydraulic
conductance)
Total surface area
What does the filtration coefficient depend on?
Water permeability per unit surface area (hydraulic
conductance)
Total surface area
How does ↑ glomerular surface area due to relaxation of the
mesangeal cells affect GFR?
↑ GFR
Reasons for increased Kf.
↑ glomerular surface area due to relaxation of the
mesangeal cells
Reasons for decreased Kf?
↑ thickness of the basement membrane (i.e., uncontrolled hypertension and diabetes mellitus)
↓ number of functional nephrons
How does decreased Kf affect GFR?
decreases GFR
Effects of afferent arteriole constriction.
↓ RPF (↓ blood inflow into the capillaries) →
↓PGC→↓netfiltrationP→ ↓ GFR
↓hydrostatic P & oncotic P in peritubular capillary → ↑ peritubular reabsorption
What are factors that would stimulate constriction of EA?
Moderate ATII
Strong sympathetic
What are the effects of EA constriction?
→ ↑ PGC → ↑ net filtration P → ↑ GFR (biphasic effect)
→ ↑ FF (↑ GFR & ↓ RPF)
↓ peritubular capillary
↓ peritubular capillary hydrostatic P, ↑ oncotic P; ↑ reabsorption
hydrostatic P; ↑ oncotic P
Describe effects of increased mean arterial BP on the kidney.
↑ MABP →↑ Capillary hydrostatic P & GFR – pressure diuresis
What are reasons for increased oncotic pressure of GC?
↑ plasma protein concentration in
the systemic blood
↓ renal plasma flow → ↑ oncotic P along glomerular capillaries
↑ FF (more than N value of 20%) Effectsof↑inoncoticPofGC:
↓ net filtration P → ↓ GFR ↓ FF
What are reasons for decreased oncotic P of GC?
Reasons: ↓ plasma protein concentration in the systemic blood (i.e., loss of proteins in the urine - nephrotic syndrome)
Effects of ↓ oncotic P of GC: ↑ net filtration P → ↑ GFR ↑ FF
What are reasons for increased Bowmans capsule hydrostatic pressure?
Reasons:
↓ urine outf low (i.e., tubular obstruction, ureteral stone or constriction)
What are the effects of increased BC hydrostatic pressure on glomerulus?
↓ net ultrafiltration P → ↓ GFR
↓ FF
Be able to reproduce this chart.
Reproduce chart.
What is the capillary hydrostatic pressure in the peritubular capillaries?
Ppc= 20 mm Hg
Why is there low capillary hyrostatic pressure in peritubular capillaries?
due to resistance of efferent arteriole
Why is there high plasma oncotic P in peritubular capillaries?
due to filtration of protein-free fluid into Bowman’s capsule
What is the plasma oncotic capillary pressure in peritubular capillaries?
35 mmHg
